That attachment screenshot is definitely misleading, and attachment upload has been delayed more than we would have liked. However, we are in the final stages of testing the funtionality now, so attachment upload for SharePoint Lists will be released in March.
Furthermore even though there might be gaps between InfoPath and PowerApps, we do strive to close them, one by one. On the other hand, PowerApps is bettering InfoPath in some areas like being able to interface with taxonomy fields in SharePoint, not to mention the mobility story. We believe that in the long run, it will be a much better replacement of InfoPath, but understand the frustrations that are being caused as we reach that point.